The present invention relates generally to instruments for measuring electrical parameters and, more particularly, to instruments, and methods employed thereby, capable of measuring continuity in an electric circuit.
Conventional techniques for troubleshooting electric circuits include making continuity tests of the circuit in which open circuit and short circuit conditions are detected. One of the simplest devices for testing continuity consists of a flashlight having a test lead. To test continuity of a conductor, for example, one end of the conductor is connected to ground and the other end is connected to the test lead. Continuity is verified when the flashlight lights. Variations of this technique include a buzzer for audible feedback confirming continuity. One drawback to this type of continuity tester is that it may not respond to fast, intermittent changes in continuity. Also, if a person using the flashlight device is not within sight or earshot of the device, that person will not detect an intermittent change in circuit continuity even though the flashlight may have responded thereto.
Another type of continuity tester includes an instrument that measures the impedance of the circuit being tested and provides a display of the impedance value. With this type of instrument, high values are indicative of open circuits and low values indicate short circuits, while intermediate values may indicate other conditions, such as the presence of poor connections in the circuit being tested. However, as with other types of prior art continuity testers, these instruments may not respond to very fast, intermittent changes in circuit continuity state. Rather, the impedance value displayed on the instrument simply represents the impedance of the circuit before or after the intermittent change. Since the instrument does not capture or display the change, a person using the instrument cannot detect the nature of the change after it has occurred. In addition, if the intermittent change is faster than the response time of the instrument's display, the change will not be detected even if the person is viewing the display when the intermittent change occurs.
Yet another type of prior art device includes conventional logic analyzers, which are high speed devices that detect and record logic changes in circuits. Continuity changes in a circuit may be thought of as logic level changes that could be detected by a logic analyzer. However, as a practical matter these devices are too sophisticated, and as a result, are too complex and expensive to be used for continuity testing. In addition, most logic analyzers are too cumbersome to be carried around for general purpose continuity testing.
Accordingly, there is a need for an instrument capable of capturing intermittent changes in continuity of an electric circuit and displaying these changes in such a way that the displays are indicative of the nature of the changes. The instrument should also be relatively inexpensive and portable so as to facilitate its use as a trouble-shooting aid. The present invention is directed to a instrument having a continuity capture feature, and a method employed thereby, designed to achieve these results.